Uncertainties, particularly in geological parameters are always present and are significant in field and reservoir development. These uncertainties could be those perceived by geologists and engineers or exist in the available data. Industry has been using uncertainty analysis to identify, address and mitigate risk. Field development strategies and well placement depend significantly on reservoir geological characterization, maturity of the depletion stage, technological factors, drive mechanism and other parameters. Well placement optimization is normally performed using a deterministic (most likely) model. The optimum placement of wells within geologic uncertainty is the issue addressed in this paper.

This paper discusses an application of the workflow performing uncertainty analysis on a sector model of a conceptual reservoir and its optimization technique of development wells under geological uncertainty. Tornado plots are used to identify the highest critical parameters among the list of uncertainties of the reservoir. Experimental Design, Proxy Model, and Monte Carlo simulation are then used to generate a density probabilistic distribution of cumulative production to identify the 10%, 50% and 90% probability (P10, P50 and P90) cases. The best field operation strategy is identified by the lowest risk (highest probability) among strategies considered. Optimum injector-producer spacing, producer-producer spacing, horizontal completion, well length and orientation are obtained at pre-defined risk level under geologic uncertainties. Results show that the optimized development plan has reduced the associated risk substantially compared to the pre-optimized case with this process.

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